Memory architecture and method of access thereto

ABSTRACT

A memory device includes control line drivers coupled to respective pairs of reference supply voltage controllers and supply voltage controllers. The control line drivers are configured to apply control signals to the reference supply voltage controllers and the supply voltage controllers. For a read operation, the reference supply voltage controllers apply a first voltage to reference voltage supply nodes of un-accessed rows of the array of memory cells and a second voltage to accessed rows. A voltage level of the first voltage is greater than a voltage level of the second voltage. For a write operation, the supply voltage controllers apply a third voltage to un-accessed rows of the array of memory cells and a fourth voltage to accessed rows. A voltage level of the third voltage is greater than a voltage level of the fourth voltage.

PRIORITY CLAIM

The present application is a divisional of U.S. application Ser. No.13/793,945, filed Mar. 11, 2013, which claims the priority of U.S.Provisional Application No. 61/720,826, filed Oct. 31, 2012, thedisclosures of which are incorporated herein by reference in theirentireties.

FIELD

The present disclosure is related to a memory architecture.

BACKGROUND

In a memory architecture, a bit line is coupled with a plurality ofmemory cells. Each of the memory cells has some leakage current when apass gate transistor in the memory cell is turned off, and draws alarger current value when the pass gate transistor is turned on. Forillustration, the leakage current when the pass gate transistor isturned off is called current Ioff while the current drawn by the memorycell when the pass gate transistor is turned on is called current Ion.The number of memory cells that can be coupled with a bit line dependson a ratio of current Ion of an accessed memory cell over currents Ioffof un-accessed memory cells. For example, as the ratio increases, anumber of memory cells coupled with the bit line increases. The memorydensity of the memory architecture is higher for a larger ratio. Incontrast, when the ratio is smaller, the number of memory cells capableof being coupled with the bit line is reduced, which reduces the memorydensity. Effectively, current Ioff of each memory cell and the ratiobased on Ion and Ioff effects the density of the memory architecture.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more embodiments of the disclosure are set forthin the accompanying drawings and the description below. Other featuresand advantages will be apparent from the description, drawings, andclaims.

FIG. 1 is a diagram of a memory array, in accordance with someembodiments.

FIG. 2 is a diagram of a memory cell of the memory array of FIG. 1, inaccordance with some embodiments.

FIG. 3 is a flowchart of a method for writing to a row of memory cell,in accordance with some embodiments.

FIG. 4 is a flowchart of a method for reading from a row of memorycells, in accordance with some embodiments.

FIG. 5 is a flowchart of a method for determining a number of memorycells coupled to a bit line, in accordance with some embodiments.

FIG. 6 is a diagram of a computer, in accordance with some embodiments.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Embodiments, or examples, illustrated in the drawings are disclosedbelow using specific language. It will nevertheless be understood thatthe embodiments and examples are not intended to be limiting. Anyalterations and modifications in the disclosed embodiments, and anyfurther applications of the principles disclosed in this document arecontemplated as would normally occur to one of ordinary skill in thepertinent art.

Some embodiments have one or a combination of the following featuresand/or advantages. In a write operation, a supply voltage value ofmemory cells in an accessed row is configured to be lower than a supplyvoltage value of memory cells in un-accessed rows. For example, theminimum supply voltage value is lower than that of an approach in whichthe supply voltage value of memory cells in the accessed row is equal tothe supply voltage value of memory cells in the un-accessed rows. Aminimum supply voltage value used in writing data to memory cells istherefore improved.

In a read operation, a supply reference voltage value of memory cells inun-accessed rows of memory cells is configured to be higher than asupply reference voltage value of memory cells in the accessed row. As aresult, a leakage current from a corresponding bit line through a passgate transistor is reduced compared with other approaches. The number ofmemory cells coupled with the bit line and the memory density istherefore increased.

For illustration, a supply voltage and a supply reference voltage arecalled a voltage VDD and a voltage VSS, respectively.

Memory Array

FIG. 1 is a diagram of a memory array 100, in accordance with someembodiments. Memory array 100 is a static random access memory (SRAM)array. Other types of memory are within the scope of variousembodiments.

Memory array 100 includes a plurality of rows and columns of memorycells 110. For illustration, N rows from row R1 to row RN, and M columnsfrom column C1 to column CM are shown. N and M are each an integernumber. For illustration, a row of memory cells 110 is called a row R,and a column of memory cells 110 is called a column C.

Each row R includes a word line (WL) driver 125 configured to provide aword line signal WLS (not labeled) on a word line WL for memory cells110 on a corresponding row R. WL driver 125 includes a buffer BFFR1 anda buffer BFFR2. Buffer BRRF1 generates a signal PWL. In someembodiments, signal PWL is generated before signal WLS is generated. Forexample, signal WLS is signal PWL delayed by a time delay provided bybuffer BFFR2. Word line WL activates a corresponding row R of memorycells 110. A supply voltage control circuit 115, based a correspondingsignal PWL, provides an internal supply voltage VDDI (not labeled) tonodes NVDDI of memory cells 110 in a corresponding row R. In someembodiments, internal supply voltage VDDI is applied to memory cells 110based on a corresponding signal PWL before memory cells 110 areactivated based on a corresponding signal WLS on word line WL. WL driver125 having two buffers BFFR1 and BFFR2 is for illustration. Otherconfigurations of WL driver 125 are within the scope of variousembodiments.

Supply voltage control circuit 115 receives supply voltage VDD andtransfers supply voltage VDD as an internal supply voltage VDDI to nodesNVDDI of memory cells 110 in a corresponding row R. In some embodiments,supply control circuit 115 provides internal supply voltage VDDI tonodes NVDDI before buffer BFFR2 activates a corresponding word line WL.Supply voltage control circuit 115 also provides a write enable signalWE to corresponding sense amplifiers 105, labeled as SA 105, whencorresponding memory cells 110 are under a write operation.

A reference supply voltage control circuit 120 receives reference supplyvoltage VSS and transfers reference supply voltage VSS as an internalreference supply voltage VSSI (not labeled) to nodes NVSSI of memorycells 110 in a corresponding row R. Supply voltage control circuit 120,based on corresponding signal PWL, provides an internal supply referencevoltage VSSI to nodes NVSSI of memory cells 110 in a corresponding rowR. In some embodiments, reference supply voltage control circuit 120provides internal supply reference voltage VSSI to memory cells 110based on a corresponding signal PWL before memory cells 110 areactivated based on a corresponding signal WLS on word line WL.

A column C includes a plurality of memory cells 110 and a senseamplifier (SA) 105. SA 105 is used to sense or read the data stored inmemory cell 110 through a bit line split of bit lines BL and ZBL in acorresponding column C. When a bit line split of bit lines BL and ZBL issufficiently developed, SA 105 is turned on to sense or amplify the bitline split and generate a full swing signal on bit lines BL and ZBL thatrepresent the data read from the corresponding memory cell 110. SA 105also receives write enable signal WE as an input. For example, whenwrite enable signal WE is activated with a high logical value,corresponding memory cells 110 are in a write operation, andcorresponding SA 105 is turned off. In contrast, when write enablesignal WE is deactivated with a low logical value, corresponding SA 105is turned on to sense data in corresponding memory cells 110.

For illustration, in a write operation when signal WE is logically high,nodes NVDDI of memory cells 110 in the accessed row R receive a voltagevalue VDDIWA (not labeled). Nodes NVDDI of memory cells in theun-accessed rows receive a voltage value VDDIWUA (not labeled). Avoltage difference between voltage value VDDIWA and VDDIWUA is calledΔVDDIW. Mathematically expressed, ΔVDDIW=VDDIWUA−VDDIWA. In someembodiments, voltage value VDDIWA is lower than voltage value VDDIWUA.Further, voltage value VDDIWUA has a VDD voltage value, such as 1.0 V,while voltage value VDDIWA is about 0.9 V. Voltage difference ΔVDDIW istherefore about 0.1 V. Other voltage values of voltage ΔVDDIW are withinthe scope of various embodiments.

In some embodiments, in a write operation, nodes NVSSI of memory cells110 in the accessed row R receive a voltage value VSSIWA (not labeled),and nodes NVSSI of memory cells 110 in the un-accessed rows R receive avoltage value VSSIWUA (not labeled). For illustration, a value ofvoltage difference between voltage value VSSIWA and VSSIWUA is calledΔVSSIW (not labeled). Mathematically expressed, ΔVSSIW=VSSIWUA−VSSIWA.In some embodiments, voltage value VSSIWA is equal to voltage valueVSSIWUA. Further, voltage value VSSIWA and voltage value VSSIWUA eachhas a VSS voltage value, such as ground or 0.0 V. Voltage ΔVSSIW istherefore about 0.0 V. Other values of voltage ΔVSSIW are within thescope of various embodiments.

For illustration, in a read operation when signal WE is deactivated,nodes NVDDI of the accessed row R receive a voltage value VDDIRA (notlabeled). Nodes NVDDI of the un-accessed rows R receive a voltage valueVDDIRUA (not labeled). A voltage difference between voltage value VDDIRAand VDDIRUA is called ΔVDDIR. Mathematically expressed,ΔVDDIR=VDDIRA−VDDIRUA. In some embodiments, voltage value VDDIRA isequal to voltage value VDDIRUA. Voltage ΔVDDIR is therefore 0 V.Further, voltage value VDDIRUA is the same as the VDD voltage value,such as 1.0 V. Explained in a different way, nodes NVDDI of both theaccessed row and un-accessed rows stay at a voltage value of supplyvoltage VDD. Other voltage values for voltage VDDIRA and VDDIRUA arewithin the scope of various embodiments.

In some embodiments, in a read operation, nodes NVSSI of accessed row Rreceive a voltage value VSSIRA (not labeled), and nodes NVDDI of theun-accessed rows R receive a voltage value VSSIRUA (not labeled). Avoltage value difference between voltage value VSSIRA and VSSIRUA iscalled ΔVSSIR. Mathematically expressed, ΔVSSIR=VSSIRUA−VSSIRA. In someembodiments, voltage value VSSIRA is lower than voltage value VSSIRUA.Further, voltage value VSSIRA has a VSS voltage value, such as ground or0 V, while voltage value VDDIRUA is about 0.1 V. Voltage ΔVSSIR istherefore about 0.1 V. Other values of voltage ΔVSSIR are within thescope of various embodiments.

Memory Cell

FIG. 2 is a diagram of a memory cell 200, in accordance with someembodiments. Memory cell 200 is an embodiment of memory cell 110 in FIG.1.

Memory cell 200 includes two P-type metal oxide semiconductor (PMOS)transistors P1 and P2, and four N-type metal oxide semiconductor (NMOS)transistors N1, N2, N3, and N4. Transistors P1, P2, N1, and N2 form across latch. Sources of transistors P1 and P2 are coupled together andserve as node NVDDI.

Each node NVDDI of a plurality of memory cells 200 is coupled togetherand receives a voltage value from a corresponding supply voltage controlcircuit 115 in FIG. 1. For example, depending on whether memory cell 200is in a read or a write operation and whether memory cell 200 is in anaccessed row R or in an un-accessed row R, node NVDDI receives acorresponding voltage value VDDIWA, VDDIWUA, VDDIRA, or VDDIRUA.

Drains of transistors P1 and N1 are coupled together and form a storagenode ND. Drains of transistors P2 and N2 are coupled together and form astorage node NDB. Gates of transistors P1 and N1 are coupled togetherand to drains of transistors P2 and N2. Gates of transistors P2 and N2are coupled together and to drains of transistors P1 and N1. Sources oftransistors N1 and N2 are coupled together and serve as node NVSSI.

Each node NVSSI of a plurality of memory cells 200 is coupled togetherand receives a voltage value from a corresponding reference supplyvoltage control circuit 120 in FIG. 1. For example, depending on whethermemory cell 200 is in a read or a write operation and whether memorycell 200 is in an accessed row R or in an un-accessed row R, node NVSSIreceives a voltage value VSSIWA, VSSIWUA, VSSIRA, or VSSIRUA.

Word line WL is coupled with a gate of each of transistors N3 and N4 ofa plurality of memory cells 200 in a row R in FIG. 1. Word line WL isalso called a write control line because a signal on word line WLcontrols transistors N3 and N4 for data on bit lines BL and ZBL to bewritten to corresponding nodes ND and NDB.

Drains of each of transistors N3 and N4 are coupled to bit lines BL andZBL, respectively. Bit lines BL and ZBL are coupled to each drain oftransistors N3 and N4 of a plurality of memory cells 200 in a column Cin FIG. 1. Each of bit lines BL and ZBL is also called a data linebecause the data carried on bit lines BL and ZBL are written tocorresponding nodes ND and NDB. In some other situations, the datastored in nodes ND and NDB are also transferred to bit lines BL and ZBLto be sensed by SA 105 in FIG. 1

Bit lines BL and ZBL serve as both data input and output for memory cell200. In some embodiments, in a write operation, applying a logical valueto a first bit line and the opposite logical value to the other bit lineenables writing the logical values at the bit lines to memory cell 200.A voltage difference between bit line BL and bit line ZBL is called abit line split. In a read operation, the data in storage nodes ND andNDB are transferred to bit lines BL and ZBL. Sensing a bit line split ofbit lines BL and ZBL reveals the data stored in memory cell 200.

For simplicity, bulks of transistors P1, P2, N1, N2, N3, and N4 inmemory cell 200 are not shown. In some embodiments, the bulks of PMOStransistors, such as transistors P1 and P2, are configured to receivesupply voltage value VDD, and the bulks of NMOS transistors, such astransistors N1, N2, N3, and N4 are configured to receive referencesupply voltage VSS.

For illustration, node ND stores a high logical value, and bit line BLis pulled to a low logical value so that node ND is written with a lowlogical value. Node NVDDI is at a source of transistor P1 and word lineWL is at gate of transistor N3. In some embodiments, in a writeoperation, voltage VDDIWA at node NVDDI of an accessed memory cell 110is applied with a voltage value lower than a high voltage value of wordline WL, which, in some embodiments, is about supply voltage VDD. As aresult, transistor P1 conducts weaker than transistor N3. Consequently,it is easier for node ND to flip to a low logical value than thesituation in which transistor P1 conducts as strong as or stronger thantransistor N3. As a result, various embodiments of the presentdisclosure are advantageous over some approaches in which voltage VDDIWAremains at supply voltage value VDD. Effectively, memory cell 200 ofvarious embodiments of the present disclosure functions at a lowervoltage VDD than some other approaches.

When node ND stores a low logical value, node NDB stores a high logicalvalue. In some embodiments, writing node ND with a high logical value isbased on writing node NDB with a low logical value. Writing node NDBwith a low logical value with reference to transistor P2, transistor N4,and bit line ZBL is similar to writing node ND with a low logical valuewith reference to transistor P1, transistor N3, and bit line BL asexplained above.

In some embodiments, in a read operation, voltage VSSIRA at node NVSSIof the accessed row R is kept at voltage value VSS, and voltage VSSIRUAat node NVSSI of un-accessed rows R is raised compared with voltagevalue VSS. For illustration, node ND stores a low logical value. Becausevoltage VSSIRUA at node NVSSI of un-accessed rows R is raised comparedwith voltage VSS, node ND is also raised. In other words, node ND has ahigher voltage value than voltage VSS or ground. In a read operation,bit line BL is pre-charged to a high logical value. In memory cells 200of un-accessed rows R, word line WL is de-activated, and transistor N3is turned off. A leakage current leaks from the high logical value ofbit line BL through transistor N3 to node ND, however. Because node NDis raised, the leakage current from bit line BL to node ND is reducedwhen compared with the situation in which a voltage value of node NVSSIand node ND is not raised, such as when voltage VSSIRUA is equal tovoltage VSS. In some embodiments, voltage VSSIRUA of un-accessed rows Ris raised to a predetermined voltage value such that the data stored inmemory cells 200 in the accessed row R continues to be reliably valid.In some embodiments, the predetermined voltage level is set such that ifvoltage VSSIRUA is raised higher than the predetermined voltage value,the data in memory cells 200 in the accessed row R is no longer bevalid.

Further, in some embodiments, the bulk of transistor N3 is at voltagevalue VSS while the source of transistor N3 or node ND is raised. As aresult, a body effect of transistor N3 raises a threshold voltage oftransistor N3, and the leakage current through transistor N3 is furtherreduced based on the body effect.

When node ND stores a high logical value, node NDB stores a low logicalvalue. In some embodiments, reading a high logical value from node ND isbased on reading a low logical value of node NDB. Reading a low logicalvalue of node NDB with references to transistor N2, transistor N4, andbit line ZBL is similar to reading a low logical value of node ND withreferences to transistor N1, transistor N3, and bit line BL as explainedabove.

Leakage Current and a Number of Memory Cells Coupled to a Bit Line

For illustration, a current flowing through transistor N3 whentransistor N3 is on is called a current Ion, and a current flowingthrough transistor N3 when transistor N3 is off is called a currentIoff. In some embodiments, transistor N3 is on when memory cell 200 isin an accessed mode, such as in a read operation. Further, transistor N3is off when memory cell 200 is in an un-accessed mode. Explained in adifferent way, in an accessed row R, transistors N3 are turned on, andin an un-accessed row R, transistors N3 are turned off. Forillustration, each column C includes N numbers of memory cells 200wherein N is an integer number. In some embodiments, with respect to acolumn C, one memory cell 200 is read accessed while N−1 memory cells200 are not read accessed. Current Ion is a current of the read accessedmemory cell 200 in column C. For illustration, the total current in N−1memory cells 200 of un-accessed rows R of column C is called Ioffcolumn.As a result, mathematically expressed, Ioffcolumn=Ioff*(N−1).

In some embodiments, a number of memory cells 200 (or 110) that can becoupled with bit line BL of a column C depends on a ratio RAT (notlabeled) of current Ion over current Ioffcolumn. When ratio RAT isincreased, a larger number of memory cells 200 can be coupled with bitline BL. In such situation, N has a larger value. In contrast, whenratio RAT is decreased, a lower number of memory cells 200 are able tobe coupled with bit line BL. In such a situation, N has a smaller value.In some embodiments, current Ion is selected to be about ten timescurrent Ioffcolumn or higher so that reading data of a memory cell 200on bit line BL is reliable. As a result, ratio RAT is about ten orhigher. If ratio RAT is less than ten, the number of memory cells 200coupled with bit line BL is reduced in some embodiments, for example. Amethod to determine the number of memory cells 200 coupled with bit lineBL is explained with reference to FIG. 5 below. In some embodimentshaving the raised VSSIRUA at a predetermined voltage value, the numberof memory cells 200 coupled with bit line BL is at least two timeshigher than approaches which do not include the raised VSSIRUA.

In the above description, bit line BL and corresponding node ND are usedfor illustration, analyses with respect to bit line ZBL andcorresponding node NDB are similar.

Writing to a Memory Cell

FIG. 3 is a flowchart of a method 300 for writing to a memory cell 200in a write accessed row R of FIG. 1, in accordance with someembodiments. For illustration, node ND stores a high logical value, andis written with a low logical value.

In operation 303, voltage control circuit 115 in accessed row R in FIG.1 generates write enable signal WE having a high logical value to putaccessed memory cell 200 in a write operation.

In operation 305, a low logical value is transferred to bit line BL, forexample, by a circuit outside of memory array 100.

In operation 310, voltage control circuit 115 in the accessed row R inFIG. 1 is configured to provide corresponding node NVDDI of memory cell200 with a voltage VDDIWA that is lower than supply voltage VDD used asa high logical value for word line WL.

In operation 312, voltage control circuits 115 of un-accessed rows R areconfigured to provide corresponding nodes NVDDI of memory cells 200 withvoltage VDDIWUA that is about supply voltage VDD.

In operation 315, word line WL of accessed row R is activated. As aresult, transistor N3 in FIG. 2 of accessed memory cell 200 in accessedrow R is turned on.

In operation 320, bit line BL corresponding to accessed memory cell 200pulls corresponding node ND to a low logical value. In other words, nodeND is written with a low logical value. Because node NVDDI of accessedmemory cell 200 has a voltage value VDDIWA lower than a high logicalvalue VDD of word line WL, transistor N3 of accessed memory cell 200conducts stronger than corresponding transistor P1. As a result, node NDflips to a low logical value easier with less contention effects fromtransistor P1. In other words, writing to node ND is easier.

Reading from a Memory Cell

FIG. 4 is a flowchart of a method 400 for reading from node ND of amemory cell 200 of a read accessed row R, in accordance with someembodiments. For illustration, node ND stores a low logical value.

In operation 405, voltage control circuit 115 in accessed row R provideswrite enable signal WE having a low logical value to place accessedmemory cell 200 in a read operation.

In operation 410, voltage control circuit 120 in accessed row R providescorresponding node NVSSI of read accessed memory cell with voltage valueVSSIRA, which is about supply voltage VSS.

In operation 415, voltage control circuits 120 in un-accessed rows Rprovide corresponding nodes NVSSI with voltage value VSSIRUA that israised compared with supply voltage VSS. In un-accessed rows R,transistors N3 are turned off, but are subject to a leakage current,however. Because voltage VSSIRUA is raised compared with voltage VSS,nodes ND of memory cells in un-accessed row R are also raised. Theleakage current through transistors N3 is therefore reduced comparedwith the situation in which voltage VSSIRUA is not raised. The bodyeffect of transistor N3 further reduces the leakage current.

In operation 420, bit lines BL and ZBL are pre-charged to a high logicalvalue.

In operation 425, WL of the read accessed memory cell 200 is activatedwith a high logical value to turn on transistor N3.

In operation 430, the low logical value of node ND pulls bit line BLtowards a low logical value. Bit line ZBL stays at the same pre-chargedhigh logical value. In other words, a bit line split between bit linesBL and ZBL starts to develop.

In operation 435, when the bit line split is sufficiently large for SA105 to sense, SA 105 is turned on. SA 105 recognizes bit line BL islower than bit line ZBL and reveals the logical data of node ND.

A Number of Memory Cells Coupled with a Bit Line

FIG. 5 is a flowchart of a method 500 for determining a number N ofmemory cells 200 coupled with bit line BL, in accordance with someembodiments. In this illustration, a memory cell 200 in an accessed rowR is used.

In operation 505, transistor N3 of memory cell 200 is turned off.

In operation 510, voltage VSSIRUA at node NVSSI of un-accessed rows R isdetermined. For example voltage VSSIRUA is selected at a voltage valuehigher than voltage VSS such that memory cell 200 fails. In other words,voltage VSSIRUA is raised, but memory cell 200 fails. In someembodiments, in such a situation, the data stored in memory cell 200 isnot reliably valid. Voltage VSSIRUA is then decreased until the datastored in memory cell 200 is reliably valid. For example, node ND storesa high logical value. Voltage VSSIUA is first selected such that thedata in node ND is not reliably logically high. Voltage VSSIUA is thendecreased until the data in node ND is reliably logically high. But ifnode ND stores a low logical value, voltage VSSIRUA is first selectedsuch that the data in node ND is not reliably logically low. VoltageVSSIRUA is then decreased until the data in node ND is reliablylogically low. Effectively, voltage VSSIRUA is raised compared withvoltage VSS, and memory 200 functions validly. In that way, the leakagecurrent in un-accessed rows R is reduced. As a result, the number ofmemory cells coupled with a bit line, such as bit BL, for example,increases. Different ways to determine voltage VSSIRUA are within thecontemplated scope of the present disclosure. For example, voltageVSSIRUA is determined based on a binary search algorithm. For anotherexample, voltage VSSIRUA is set at 0 V and increased until the datastored in memory cell 200 is not reliably valid, and a value of voltageVSSIRUA prior to the data stored in memory cell 200 is not reliablyvalid is used in memory array 100.

In operation 515, a worst-case current leaked through transistor N3 isconsidered current Ioff. Alternatively stated, current Ioff isdetermined. In some embodiments, current Ioff is available based oncharacteristics of transistor N3. In some other embodiments, currentIoff is determined by simulation.

In operation 520, current Ion is determined. In some embodiments,current Ion is available based on characteristics of transistor N3. Insome other embodiments, current Ion is determined by simulation.

In operation 525, a value for ratio RAT is chosen. For example, ratioRAT being at least 10 is applicable, and the value 10 is chosen. Forillustration, RATVALMIN refers to the minimum value of ratio RAT, and is10 in this example.

Another value of ratio RAT different from 10 is within the scope ofvarious embodiments. Mathematically expressed,

RAT=Ion/Ioffcolumn>=10 or

Ion/((Ioff)*(N−1))>=10 or

N<=(Ion/(10*Ioff))+1  (1)

In operation 530, a value of integer N is selected based on equation(1). For example, integer N is selected to be equal to(Ion/(10*Ioff))+1.

In some embodiments, the number N is determined for one column and isused for all columns of memory array 100. In other words, each column Cof memory array 100 has a same number of N memory cells 200.

Computer

FIG. 6 is a functional block diagram of a computer system 600, inaccordance with some embodiment. In some embodiments, computer 600 isused to implement various methods of the present disclosure, including,for example, methods 300, 400, and 500 in FIGS. 3, 4, and 5,respectively.

A controller 610 controls logic, processes information, and coordinatesactivities of computer system 600. For example, controller 610 isconfigured to execute computer program code 622 to cause computer 600 toimplement methods 300, 400, and 500. In some embodiments, controller 610is a central processing unit (CPU), a multi-processor, a distributedprocessing system, an application specific integrated circuit (ASIC),and/or a suitable processing unit.

Computer readable storage medium 620 includes program code or a set ofexecutable instructions 622. Storage medium 620 also stores informationincluding, for example, information used to perform methods 300, 400,and 500, information generated during performing methods 300, 400, and500, etc. In some embodiments, storage medium 620 is a non-transitorystorage medium.

In some embodiments, storage medium 620 is an electronic, magnetic,optical, electromagnetic, infrared, and/or a semiconductor system,apparatus, or device. For example, storage medium 620 includes asemiconductor or solid-state memory, a magnetic tape, a removablecomputer diskette, a random access memory (RAM), a read-only memory(ROM), a rigid magnetic disk, and/or an optical disk. In someembodiments, storage medium 620 includes a compact disk-read only memory(CD-ROM), a compact disk-read/write (CD-R/W), and/or a digital videodisc (DVD).

An input-output interface 630 enables a programmer to provide data tocomputer system 600, to manipulate computer system 600 to performmethods 300, 400, and 500, for example.

A display 640 displays information to users of computer 600, including,for example, a status of operations of methods 300, 400, and 500. Insome embodiments, display 640 includes a graphical user Interface (GUI).In some embodiments, input-output interface 630 and display 640 enable auser to operate computer system 600 in an interactive manner.

A network interface 650 enables computer system 600 to communicate witha network 660, to which one or more other computer systems areconnected. Network interface 650 includes wireless network interfacessuch as BLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA. Alternatively and/oradditionally network interface 650 includes a wired network interfacesuch as an ETHERNET, USB, or IEEE-1394 port. In some embodiments,computer system 600 and at least one computer on network 660 operate toperform functions of computer system 600 as describe above.

In some embodiments of a method of accessing a memory array, during awrite operation a write enable signal is set to a first logical valueand during a read operation the write enable signal is set to a secondlogical value different from the first logical value. A first word linesignal corresponding to an accessed row of the memory array is set to athird logical value, and a second word line signal corresponding to anun-accessed row of the memory array is set to a fourth logical valuedifferent from the third logical value. A supply voltage of the accessedrow is set to either a first supply voltage value or a second supplyvoltage value based on the write enable signal and the first word linesignal. A supply voltage of the un-accessed row is set to either thefirst supply voltage value or the second supply voltage value based onthe write enable signal and the second word line signal.

In some embodiments a memory device includes a memory array having amemory cell in a row of a column of memory cells. A supply voltagecontroller is coupled to a voltage supply node of the memory cell. Thesupply voltage controller is configured to apply a first voltage to thevoltage supply node of the memory cell if the row of the column ofmemory cells is an un-accessed row for a write operation and apply asecond voltage to the voltage supply node of the memory cell if the rowof the column of memory cells is an accessed row for the writeoperation. A voltage level of the first voltage is greater than avoltage level of the second voltage.

In some embodiments a memory device includes a memory array having amemory cell in a row of a column of memory cells. A reference supplyvoltage controller is coupled to a reference voltage supply node of thememory cell. The reference supply voltage controller is configured toapply a first voltage to the reference voltage supply node of the memorycell if the row of the column of memory cells is an un-accessed row fora read operation and apply a second voltage to the reference voltagesupply node of the memory cell if the row of the column of memory cellsis an accessed row for the read operation. A voltage level of the firstvoltage is greater than a voltage level of the second voltage.

A number of embodiments have been described. It will nevertheless beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure. For example, various transistorsbeing shown as a particular dopant type, such as an N-type or a P-typeMetal Oxide Semiconductor (NMOS or PMOS), are for illustration purposes.Embodiments of the disclosure are not limited to a particular type.Selecting different dopant types for a particular transistor is withinthe scope of various embodiments. A low or high logical value of varioussignals used in the above description is also for illustration. Variousembodiments are not limited to a particular logical value when a signalis activated and/or deactivated. Selecting different logical values iswithin the scope of various embodiments. In various embodiments, atransistor functions as a switch. A switching circuit used in place of atransistor is within the scope of various embodiments. In variousembodiments, a source of a transistor can be configured as a drain, anda drain can be configured as a source.

The above illustrations include exemplary steps, but the steps are notnecessarily performed in the order shown. Steps may be added, replaced,changed order, and/or eliminated as appropriate, in accordance with thespirit and scope of disclosed embodiments.

What is claimed is:
 1. A method of accessing a memory array, comprising:during a write operation of the memory array, setting a write enablesignal to a first logical value; during a read operation of the memoryarray, setting the write enable signal to a second logical valuedifferent from the first logical value; setting a first word line signalcorresponding to an accessed row of the memory array to a third logicalvalue; setting a second word line signal corresponding to an un-accessedrow of the memory array to a fourth logical value different from thethird logical value; selectively setting a supply voltage of theaccessed row to a first supply voltage value or a second supply voltagevalue based on the write enable signal and the first word line signal;and selectively setting a supply voltage of the un-accessed row to thefirst supply voltage value or the second supply voltage value based onthe write enable signal and the second word line signal.
 2. The methodof claim 1, wherein: selectively setting the supply voltage of theaccessed row comprises setting the supply voltage of the accessed row tothe first supply voltage value if the write enable signal has the firstlogical value and the first word line signal has the third logicalvalue, selectively setting the supply voltage of the un-accessed rowcomprises setting the supply voltage of the un-accessed row to thesecond supply voltage value if the second word line signal has thefourth logical value, and the first supply voltage value is less thanthe second supply voltage value.
 3. The method of claim 1, furthercomprising: selectively setting a reference voltage of the accessed rowto a first reference voltage value or a second reference voltage valuebased on the first word line signal; and selectively setting a referencevoltage of the un-accessed row to the first reference voltage value orthe second reference voltage value based on the second word line signal.4. The method of claim 3, wherein: selectively setting the referencevoltage of the accessed row comprises setting the reference voltage ofthe accessed row to the first reference voltage value if the first wordline signal has the third logical value; and selectively setting thereference voltage of the un-accessed row comprises setting the referencevoltage of the un-accessed row to the second reference voltage value ifthe second word line signal has the fourth logical value, wherein thefirst reference voltage value is less than the second reference voltagevalue.
 5. A memory device comprising: a memory array comprising a memorycell in a row of a column of memory cells; and a supply voltagecontroller coupled to a voltage supply node of the memory cell andconfigured to: apply a first voltage to the voltage supply node of thememory cell if the row of the column of memory cells is an un-accessedrow for a write operation to the memory array, and apply a secondvoltage to the voltage supply node of the memory cell if the row of thecolumn of memory cells is an accessed row for the write operation to thememory array, wherein a voltage level of the first voltage is greaterthan a voltage level of the second voltage.
 6. The memory device ofclaim 5 further comprising a control line driver coupled to the supplyvoltage controller, wherein the supply voltage controller is configuredto be responsive to a first signal received from the control line driverto apply the first voltage to the voltage supply node of the memorycell, and responsive to a second signal received from the control linedriver to apply the second voltage to the voltage supply node of thememory cell.
 7. The memory device of claim 6 wherein the control linedriver is configured to: apply the first signal to the supply voltagecontroller if the row of the column of memory cells is the un-accessedrow, and apply the second signal to the supply voltage controller if therow of the column of memory cells is the accessed row.
 8. The memorydevice of claim 6 wherein the control line driver comprises: a firstbuffer coupled to a control line of the memory array; and a secondbuffer coupled to the first buffer, a reference supply voltagecontroller, and the supply voltage controller.
 9. The memory device ofclaim 8 wherein the supply voltage controller is configured to beresponsive to a third signal received from the second buffer to applythe first voltage to the voltage supply node of the memory cell beforethe first buffer activates the control line.
 10. The memory device ofclaim 5 comprising a reference supply voltage controller configured to:apply a third voltage to a reference voltage supply node if the row ofthe column of memory cells is the un-accessed row for the writeoperation, and apply a fourth voltage to the reference voltage supplynode if the row of the column of memory cells is the accessed row forthe write operation, wherein a voltage level of the third voltage isequal to a voltage level of the fourth voltage.
 11. The memory device ofclaim 5 wherein the memory cell comprises: a first storage nodeassociated with a first data line; and a second storage node associatedwith a second data line, wherein the first data line and the second dataline are configured for both writing to and reading from the memorycell.
 12. The memory device of claim 5 wherein: the memory cell includesa first transistor of a first type, a second transistor of the firsttype, a first transistor of a second type, and a second transistor ofthe second type, a terminal of the first transistor of the first typeand a terminal of the second transistor of the first type are coupledtogether and configured to serve as the voltage supply node of thememory cell, and a terminal of the first transistor of the second typeand a terminal of the second transistor of the second type are coupledtogether and configured to serve as a reference voltage supply node ofthe memory cell.
 13. A memory device comprising: a memory arraycomprising a memory cell in a row of a column of memory cells; and areference supply voltage controller coupled to a reference voltagesupply node of the memory cell and configured to: apply a first voltageto the reference voltage supply node of the memory cell if the row ofthe column of memory cells is an un-accessed row for a read operationfrom the memory array, and apply a second voltage to the referencevoltage supply node of the memory cell if the row of the column ofmemory cells is an accessed row for the read operation from the memoryarray, wherein a voltage level of the first voltage is greater than avoltage level of the second voltage.
 14. The memory device of claim 13further comprising a control line driver coupled to the reference supplyvoltage controller, wherein the reference supply voltage controller isconfigured to be responsive to a first signal received from the controlline driver to apply the first voltage to the reference voltage supplynode of the memory cell, and responsive to a second signal received fromthe control line driver to apply the second voltage to the referencevoltage supply node of the memory cell.
 15. The memory device of claim14 wherein the control line driver is configured to: apply the firstsignal to the reference supply voltage controller if the row of thecolumn of memory cells is the un-accessed row, and apply the secondsignal to the reference supply voltage controller if the row of thecolumn of memory cells is the accessed row.
 16. The memory device ofclaim 14 wherein the control line driver comprises: a first buffercoupled to a control line of the memory array; and a second buffercoupled to the first buffer, a supply voltage controller, and thereference supply voltage controller.
 17. The memory device of claim 16wherein the reference supply voltage controller is configured to beresponsive to a third signal received from the second buffer to applythe first voltage to the reference voltage supply node of the memorycell before the first buffer activates the control line.
 18. The memorydevice of claim 13 comprising a supply voltage controller configured to:apply a third voltage to a voltage supply node if the row of the columnof memory cells is the un-accessed row for the read operation, and applya fourth voltage to the voltage supply node if the row of the column ofmemory cells is the accessed row for the read operation, wherein avoltage level of the third voltage is equal to a voltage level of thefourth voltage.
 19. The memory device of claim 13 wherein the memorycell comprises: a first storage node associated with a first data line;and a second storage node associated with a second data line, whereinthe first data line and the second data line are configured for bothwriting to and reading from the memory cell.
 20. The memory device ofclaim 13 wherein: the memory cell includes a first transistor of a firsttype, a second transistor of the first type, a first transistor of asecond type, and a second transistor of the second type, a terminal ofthe first transistor of the first type and a terminal of the secondtransistor of the first type are coupled together and configured toserve as a voltage supply node of the memory cell, and a terminal of thefirst transistor of the second type and a terminal of the secondtransistor of the second type are coupled together and configured toserve as the reference voltage supply node of the memory cell.